(Applicant's Abstract) Clinical manifestations of asthma result in part from chronic inflammation that leads to mucous cell metaplasia (MCM), the appearance of mucous cells in peripheral airways that are normally devoid of these cells. In a mouse model of asthma, systemic immunization with ovalbumin (OVA) followed by repeated exposures to OVA aerosols initially induces inflammation and MCM that resemble those found in humans with allergic asthma. However, in contrast to humans, repeated exposures of mice to allergen for a prolonged period causes inflammation and MCM to decrease from previous peak levels. The state of apparent resolution in rodents has been associated with the termination of Th2 responses and coincident appearance of IFNgamma-producing T lymphocytes. The goal of this application is to identify the immune mediators involved in the development and resolution of metaplastic mucous cells so that new approaches can be exploited to reduce mucous cell numbers in asthmatics. In Aim 1, we will test the hypothesis that after exposure to allergen for a limited time, T-lymphocytes, mast cells and their inflammatory mediators induce MCM by directly affecting the airway epithelium. Thl, Th2, or mast cells, with and without cross-linking their high affinity IgE receptor, and their inflammatory mediators will be added selectively to an organ culture system comprised of microdissected bronchiolar explants to mimic the conditions in vivo. Tissues from IL-4Ralpha and Stat6-knockout mice will be used to evaluate whether these proteins in airway epithelial cells signal mucin biosynthesis and storage. In Aim 2, we will test the hypothesis that reduction of MCM in mice following repeated exposures to allergen for a prolonged period results from induction of pro-apoptotic regulators in mucous cells causing cell death. We will determine whether IFNgamma is responsible for the observed expression of the pro-apoptotic Bax, and evaluate the role of Bax or other apoptotic regulators in causing cell death. The application of these findings to human asthmatics will be tested in Aim 3. We will test the hypothesis that inflammatory mediators from asthmatics suppress expression of Bax and enhance mucous cell survival. The difference in the percentage of Bax-expressing cells between controls and mild asthmatics will be investigated using autopsy tissues and bronchial brushings. Furthermore, the effect of bronchoalveolar lavage fluid obtained from mild asthmatics and controls inducing MCM and Bax expression in human bronchial epithelial cells will be determined. These studies will provide new strategies to reduce mucous cell numbers in asthmatic patients.